The invention relates generally to sine wave generators and, more particularly, to a sine wave generator capable of producing single or multi-tone analog signals comprised of sine waves programmable in frequency, amplitude, and initial phase.
Sine wave generators are used for many different applications, e.g., testing the AC characteristics of integrated circuits such as operational amplifiers and active and passive filters. However, conventional generators typically form sine waves using analog components, and such components ordinarily must be controlled manually. Accordingly, these generators lack the flexibility required for modern digital data processing applications.
To take advantage of the processing capability and flexibility of modern digital computers, programmable sine wave generators have been devised. In these prior art systems, discrete points on a sine wave are generated in digital form by a microprocessor or an array processor and communicated to a digital-to-analog converter wherein an analog signal is formed from the digital data. The programming for these generators is implemented in either software or microcode, and the algorithms frequently use table look-up routines to generate the digital data. Because of the software based nature of such generators and the time required for the code to execute, the process does not operate fast enough for real time applications. Consequently, those prior art systems must use a memory to store a pre-generated representation of a sine wave, and the data stored in the memory then is clocked out to a digital-to-analog converter at a prescribed rate. If a low distortion sine wave is desired then a substantial amount of memory must be provided for storing enough data points (particularly at higher frequencies). To vary the output frequency of the resulting signal, the output clock is varied by a phase locked loop circuit, with the concomitant phase jitter problems. Alternatively the output frequency is varied by dividing a very high frequency clock, but the high frequency clock often interferes with the analog circuitry.